The present invention relates to an image forming apparatus that is applicable, for example, as a color printer, a color copying machine or a color facsimile. More specifically, the present invention relates to a color electrophotographic apparatus for forming color images by electrophotography, and to an image forming unit used in the same.
A conventional image forming apparatus is disclosed, for example, in Publication of Unexamined Patent Application (Tokkai) No. Hei 7-36246.
The following is an explanation of a conventional color image forming apparatus as disclosed in the same publication, with reference to FIG. 43. As shown in FIG. 43, an intermediate transfer belt unit 101 includes an intermediate transfer belt 102, a primary transfer roller 103, a secondary transfer roller 104, a cleaner roller 105, and a waste toner reservoir 106. Color images can be superimposed on the transfer belt 102. In the middle of the main body of this image forming apparatus, a group of image forming units 108 is provided. Four image forming units 107Bk, 107Y, 107M and 107C for black, yellow, magenta and cyan, each unit being of sector shape in cross section, are arranged circularly to form the group of image forming units 108. When an image forming unit 107Bk, 107Y, 107M or 107C is installed properly in the color image forming apparatus, mechanical driving systems and electrical connection systems are coupled between the image forming units 107Bk, 107Y, 107M and 107C and other portions of the color image forming apparatus via mutual coupling members, so that both sides are mechanically and electrically connected. The image forming units 107Bk, 107Y, 107M and 107C are supported by a supporter and collectively rotated by a motor, so that they can revolve around a non-rotatable cylindrical shaft 109. For image formation, the image forming units 107Bk, 107Y, 107M and 107C are successively moved by rotation to an image forming position 110, where they oppose the primary transfer roller 103 spanning the intermediate transfer belt 102. The image forming position 110 is also the exposure position for exposure with a laser signal beam 111.
Inside this image forming apparatus, a laser exposing device 112 is arranged horizontally below the group of image forming units 108. The laser signal beam 111 passes through a light path opening 113 between the image forming units 207M and 207C, and through an opening provided in the shaft 119, and enters a mirror 114, which is fixed inside the shaft 119. The laser signal beam 111 reflected by the mirror 114 enters the black image forming unit 107Bk positioned at the image forming position 110 through an exposure opening 115. Then, the laser signal beam 111 passes through a light path between a developing device 116 and a cleaner 117, arranged on the upper and the lower side in the image forming unit 107Bk, enters an exposure portion on the left side of a photosensitive member 118, and scans for exposure along the direction of the axis of the photosensitive member 118. The toner image formed on the photosensitive member 118 is transferred to the intermediate transfer belt 102. Then, the group of image forming units 108 rotates 90 degrees, so that the yellow image forming unit 107Y moves into the image forming position 110. An operation similar to the above formation of the black image is performed to form a yellow toner image overlaying the black toner image previously formed on the intermediate transfer belt 102. Similar operations as explained above are performed using the magenta and cyan image forming units 107M and 107C to compose a full color image on the intermediate transfer belt 102. After the full color image on the intermediate transfer belt 102 is completed, a recording paper is conveyed by a secondary transfer roller 104 and a tertiary transfer roller 119, and the color image is simultaneously transferred onto the recording paper. The recording paper onto which the color image has been transferred is conveyed to a fuser 120, which fuses the color image on the recording paper.
The above relates to an image forming apparatus as disclosed in Tokkai Hei 7-36246 etc., but these prior art examples do not disclose particular structures for retaining the image forming units precisely and reliably in the image forming apparatus, so that there is a need for the realization of such technological means.
Moreover, a color image forming apparatus for forming a color image with four image forming units by superimposing toner images on an intermediate transfer belt is known from Tokkai Hei 9-304996.
The following is an explanation of the conventional color image forming apparatus disclosed in this publication, with reference to FIGS. 44 and 45. FIG. 44 is a cross sectional view showing a positioning and driving mechanism for a photosensitive member in a conventional color image forming apparatus. FIG. 45 is a perspective view of the same.
As shown in FIGS. 44 and 45, flanges 402 are attached to both end portions of a drum-shaped photosensitive member 401, and one photosensitive member shaft 403 is attached to both flanges 402. A concave tapered surface 404 is formed on the right end of the photosensitive member shaft 403, and a coupling plate 406 having eight tongues 405 is attached around the photosensitive member shaft 403 forming the concave tapered surface 404. Thus, the photosensitive member 401 can be rotated by rotating the coupling plate 406.
The photosensitive member driving mechanism, which is provided at the apparatus main body, comprises a driving shaft 411, a coupling plate 412 rotating together with the driving shaft 411, a driving gear 413, and a driving motor. On the tip of the driving shaft 411, a convex tapered surface 414 is formed, which mates with the convex tapered surface 404 formed on the right end of the photosensitive member shaft 403.
The coupling plate 412 is provided with eight coupling tongues 418, which mesh with the coupling plate 406 on the side of the photosensitive member 401. The coupling plate 412 is fixed in rotation direction to the driving shaft 411 by a pin 415, but the coupling plate 412 is movable in the axial direction within a predetermined distance. Thus, the coupling plate 412 retreats temporarily when the tips of the coupling tongues 418 abut the tips of the coupling tongues 405. The coupling plate 412 is forced by a compression spring 416 to abut a tip stopper 417, which holds it in a certain position.
The driving shaft 411 is supported rotatably and displaceably in the thrust direction by bearings 422 that are fixed to a hosing-side plate 420 and a driving base plate 421. A driving shaft gear 413 meshing with a motor-side gear 423 is attached to the driving shaft 411 between the housing-side plate 420 and the driving base plate 421. A compression spring 424 is inserted between the bearing 422 and the driving shaft gear 413, and this compression spring 424 biases the driving shaft 411 in a direction separating it from the photosensitive member 401. By moving a thrust bearing 425, the driving shaft 411 can be moved against the force of the compression spring between a separated position and a coupling position
When the image forming unit in the image forming position is being changed, the driving shaft 411 is positioned in a separated position, where it is separated from the photosensitive member shaft 403. Then, during the image forming operation, the driving shaft 411 is positioned in a coupling position, where the concave tapered surface 401 is coupled with the convex tapered surface 414, as shown in FIG. 44. In this coupling position, the coupling tongues 405 mesh with the coupling tongues 418, so that a driving force can be transmitted.
The above relates to a color image forming apparatus as disclosed for example in Tokkai Hei 9-304996, but in order to suppress relative positional misalignments in such a color image forming apparatus, there is a need for reliability and reproducibility of the positioning of the photosensitive member in this image forming apparatus as well as the matching of rotational speed variations. Moreover, there is also a need for making the apparatus smaller.
However, in such conventional configurations, the coupling portions are easily misaligned, and the retention of the photosensitive member is unreliable, which causes the problem that the precision of the positioning of the photosensitive member is low, and there are variations in the position of the photosensitive member due to external forces such as the driving force for the photosensitive member and the developing device.
The reason for these problems is that the concave tapered surface 404 and the convex tapered surface 414 have the same shape and mate with each other. It is difficult to make the photosensitive member 401 and the driving shaft 411 completely coaxial at the image forming position. As is shown in FIG. 46, if the central axes of the driving shaft 411 and the photosensitive member shaft 403 are tilted against each other, their two cone-shaped surfaces cannot be contacted over the entire peripheral direction. In this case, the concave tapered surface 404 and the convex tapered surface 414 contact each other only at the two points P1 and P2, of which P1 is on a surface including the two tilting center axes. If the concave tapered surface 404 and the convex tapered surface 414 contact each other only at two points like this, the contact area is small, so that the coupling portion easily shifts away, and the retention of the photosensitive member 401 becomes unreliable. Moreover, the rotation center of the photosensitive member 401 cannot be positioned with good reproducibility.
Moreover, in order to press the long convex tapered surface 414 against the concave tapered surface 404, the stroke over which the driving shaft 411 is shifted becomes long. As a result, a large waiting space has to be provided in the width direction inside the apparatus, which causes the problem that the width of the apparatus housing becomes larger, so that the apparatus main body becomes undesirably large.
Moreover, when the driving shaft 411 rotates the photosensitive member 401, a counterforce against the rotation driving acts on the tapered coupling portion. Thus, an unreliable coupling portion will shift away, and the rotation center of the photosensitive member 401 shifts undesirably. Moreover, when the coupling portions of the photosensitive member shaft 403 and the driving shaft 411 are misaligned, the rotation speed of the photosensitive member 401 changes, which causes the problem that the positions at which the colors are superimposed on the intermediate transfer belt vary for each color.
Moreover, when the center axes of the photosensitive member shaft 403 and the driving shaft 411 are misaligned, the difference in the angular speed that is transmitted from the driving shaft 411 to the photosensitive member shaft 403 increases, which causes the problem that the positions at which the colors are superimposed on the intermediate transfer belt vary for each color.
Moreover, when the center axes of the photosensitive member shaft 403 and the driving shaft 411 are misaligned, the contact points between the coupling tongues 405 and 418 cannot be adjusted precisely, which causes the problem that the difference in the shapes of the contacting surfaces causes variations in the rotation speed for the photosensitive member 401, and the speed variations are different for each color.
Moreover, since the coupling tongues 405 and 418 that establish contact during the rotation driving change, there is the problem that variations in the pitch between the coupling tongues 405 and 418 cause variations in the angular speed of the photosensitive member 401, and as a result, different rotation variations are caused for each color, and relative positional misalignments occur for each color.
Moreover, while the driving shaft 411 is being moved toward the photosensitive member 401, when the tips of the coupling tongues 405 hit the tips of the coupling tongues 418, the photosensitive member 401 is moved in a direction that is perpendicular to the rotation axis so that the concave tapered surface 404 moves, and the driving shaft 411 cannot be coupled with the concave tapered surface 404, and as a result, there is the problem that it becomes impossible to position the photosensitive member 401 and to rotate
Moreover, since the angle of the concave tapered surface 404 and the convex tapered surface 414 is large, there is the problem that their coupling becomes incomplete and unreliable. Furthermore, since the aperture circle at the end portion of the concave tapered surface 404 is small, sometimes it becomes impossible to insert the driving shaft 411 into the concave tapered surface 404.
Moreover, in order to make the coupling plate 412 movable on the driving shaft, a clearance is provided between the coupling plate 412 and the driving shaft 411, but to suppress too much play between the coupling plate 412 and the driving shaft 411, the sliding fitting portion between the coupling plate 412 and the driving shaft 411 has to be made long. As a result, there is the problem that the distance from the bearing 422 of the driving shaft 411 to the tip becomes longer, and the width of the apparatus housing becomes larger, so that the apparatus main body becomes undesirably large.
Moreover, when the driving shaft 411 moves in the direction of the photosensitive member 401, the inner peripheral surface of the coupling tongues 418 on the side of the driving shaft 411 may abut the outer peripheral surface of the coupling tongues 405 on the side of the photosensitive member 401, which causes the problem that the photosensitive member 401 cannot be moved in a direction perpendicular to the rotation axis. Moreover, conversely, the outer peripheral surface of the coupling tongues 418 on the side of the driving shaft 411 may abut the inner peripheral surface of the coupling tongues 405 on the side of the photosensitive member 401, which causes the problem that the photosensitive member 401 cannot be positioned in its proper position, even if pressure is applied to the driving shaft 411.
Moreover, load variations due to the meshing of the coupling tongues 405 and 418 bring about speed variations of the intermediate transfer belt, which causes the problem that the positions of the images that are superimposed on the intermediate transfer belt become misaligned.
It is an object of the present invention to solve the problems of the prior art, and to provide an image forming apparatus for outputting color images that successively changes a plurality of image forming units, wherein the image forming units can be retained precisely and reliably at their proper position within the image forming apparatus main body, and which can output high-quality images, and to provide an image forming unit for the same.
Moreover, it is an object of the present invention to provide a small image forming apparatus and image forming unit used in the same, wherein the reproducibility of the positioning of the photosensitive member in the image forming position as well as the conformance of the rotation speed variations for each color are improved, and with which relative positional misalignments for each color can be suppressed.
In order to achieve these objects, a first configuration of an image forming apparatus in accordance with the present invention comprises a plurality of image forming units having a rotator; image forming unit conveying means for switching the plurality of image forming units by moving them successively between an image forming position and a waiting position; a rotator support member for positioning the rotator that is in the image forming position in a proper position in an apparatus main body by coupling with at least one axial end portion of the rotator in the axial direction of the rotator and supporting the image forming units in a freely rotatable manner; and a rotation stop portion for positioning the rotational orientation of an axis of the rotator of the image forming units.
Examples of suitable rotators include a photosensitive member or a developing roller.
With this first configuration of an image forming apparatus, it is possible to precisely and reliably retain image forming units at their proper position in the apparatus main body with a simple configuration, even when a plurality of different image forming units is used. As a result, it is possible to realize an image forming apparatus that can output high-quality color images.
Moreover, it is preferable that the image forming apparatus according to the first configuration further comprises a rotator driving means for driving the rotator, the rotation stop portion being provided on the same side of the rotator in the axial direction as the rotator driving means. With this preferable configuration, it is possible to concentrate the parts on which loads act close to each other, so that by raising the precision and the robustness of these parts, the positioning can be made more reliable. As a result, it is possible to realize an image forming apparatus that can output high-quality color images. Moreover, it is preferable that one supporting position of the rotator axis, a driving force transmission position for driving force transmission with the driving means, and a rotation stop position for stopping rotation with the rotation stop portion are substantially on the same plane, which is perpendicular to the axis of the rotator. With this preferable configuration, the torque on one support position of the axis is cancelled, and the driving force due to the driving means hardly influences the other support position of the axis, so that it is possible to precisely and reliably retain image forming units at their proper position in the apparatus main body with a simple configuration. As a result, it is possible to realize an image forming apparatus that can output high-quality color images.
Moreover, it is preferable that in the image forming apparatus according to the first configuration, the rotator is a photosensitive member; the image forming units further comprise a developer, which is driven by a developer driving means; and the rotation stop portion is provided on the same side of the rotator in an axial direction as the developer driving means. With this preferable configuration, it is possible to concentrate the parts on which loads act even closer to each other, so that by raising the precision and the robustness of these parts, the positioning can be made more reliable. As a result, it is impossible to realize an image forming apparatus that can output high-quality color images. Moreover, in this case, it is preferable that one supporting position of the rotator axis, a driving force transmission position for driving force transmission with the driving means, and a rotation stop position for stopping rotation with the rotation stop portion are substantially on the same plane, which is perpendicular to the axis of the rotator.
Moreover, it is preferable that in the image forming apparatus according to the first configuration, the rotation stop portion stops the rotation of the image forming units on a surface that is substantially parallel to a line connecting the axis of the rotator and a rotation stop position. With this preferable configuration, no excessive counter-forces act on the support portion of the rotator axis, so that the rotator can be retained even more reliably.
Moreover, it is preferable that in the image forming apparatus according to the first configuration, the rotator is a photosensitive member; the image forming apparatus further comprises a developer and a developer driving means for driving the developer; and the rotation stop portion stops the rotation of the image forming units on a surface that is substantially parallel to a direction of a driving force exerted by the developer driving means. With this preferable configuration, no excessive counter-forces act on the support portion of the rotator axis, so that the rotator can be retained even more reliably. Moreover, in this case, it is preferable that the rotation stop portion stops the rotation of the image forming units near an action line of the driving force exerted by the developer driving means. With this preferable configuration, there are almost no excessive counter-forces on the support portion of the rotator axis, so that the rotator can be retained even more reliably.
Moreover, it is preferable that in the image forming apparatus according to the first configuration, the rotation stop portion is provided in the image forming unit conveying means. With this preferable configuration, a rotation stop portion can be provided at a position close to the image forming unit, so that the rotation of the image forming unit can be stopped reliably without providing, for example, a large protrusion in the image forming unit or the apparatus main body.
Moreover, it is preferable that in the image forming apparatus according to the first configuration, the rotator is a photosensitive member; the image forming apparatus further comprises a developer, a developer driving means for driving the developer, and a photosensitive member driving means for driving the photosensitive member; and at the time of image formation, the developer driving means starts to drive the developer after the photosensitive member driving means has started to drive the photosensitive member. With this preferable configuration, it is possible to precisely and reliably retain image forming units at their proper position in the apparatus main body with a simple configuration, even when the rotator axis is not sufficiently supported. As a result, it is possible to realize an image forming apparatus that can output high-quality color images.
Moreover, it is preferable that the image forming apparatus according to the first configuration further comprises a thrust stop portion for positioning the axial direction of the rotator of the image forming units, which is provided near the axis of the rotator. With this preferable configuration, the torque on the support position of the rotator axis becomes small, so that it is possible to smoothly support the axis, even when the image forming unit is tilted. Moreover, in this case, it is preferable that the rotation stop portion and the thrust stop portion are provided on the same side of the rotator in the axial direction. With this preferable configuration, the members relating to the positioning can be concentrated close to each other, so that the positioning precision can be improved.
Moreover, it is preferable that in the image forming apparatus according to the first configuration, the rotator is a photosensitive member; the image forming apparatus further comprises a developer, a developer driving means for driving the developer, and a photosensitive member driving means for driving the photosensitive member; and the direction of the torque on the axis of the photosensitive member due to the gravitational force of the image forming unit acting on the image forming unit is opposite to the direction of the torque on the axis of the photosensitive member due to the developer driving means, and the size of the torque due to the gravitational force of the image forming unit is smaller than the size of the torque due to the driving gear for the developer. With this preferable configuration, the rotation stop force of the image forming unit on the rotation stop portion is reduced, and the influence of gravity is reduced, so that a more reliable positioning becomes possible.
A first configuration of an image forming unit in accordance with the present invention comprises a rotator. The image forming unit is retained in a manner that it can be installed in or removed from an apparatus main body; a rotator support member on an apparatus main body side is coupled with at least one axial end portion of the rotator positioned in an image forming position, in the axial direction of the rotator to position the rotator in a proper position in an apparatus main body; and positioning of the rotational orientation of an axis of the rotator is performed with a rotation stop portion on the side of the apparatus main body. With this first configuration of an image forming unit, it is possible to realize an image forming unit that can be retained precisely and reliably at a proper position in the apparatus main body.
A second configuration of an image forming apparatus in accordance with the present invention comprises a plurality of image forming units having a rotator with flanges on both ends; a unit retaining member, which retains the plurality of image forming units, and switches the plurality of image forming units by moving them successively between an image forming position and a waiting position; an intermediate transfer member, which contacts the image forming unit positioned in the image forming position and successively accepts toner images of various colors from the image forming units, so as to form a colored toner image on its surface; and a positioning member for coupling with at least one of the flanges of the rotator by advancing and receding in the axial direction when being substantially coaxial with the rotator of the image forming unit that is positioned in the image forming position; wherein a coupling part for coupling with the positioning member is provided at the center of end surfaces of the flanges; wherein the coupling part is a concave tapered surface with a circular cross section having the axis of the rotator as a center axis; and wherein a tip of the positioning member is a convex spherical surface, whose rotation center is the center axis. With this second configuration of an image forming apparatus, it is possible even when the positioning member and the rotator are coupled while their axes are tilted against each other, the contact portions of the coupling portions are circles formed by the intersection between a plane perpendicular to the axis of the rotator and the concave tapered surface. Consequently, the rotator can be held and controlled over the entire periphery. As a result, it is possible to hold and position the rotator reliably.
It is preferable that in the image forming apparatus according to the second configuration, the tip of the concave tapered surface at the coupling part contacting the positioning member during positioning and coupling is provided with a tapered surface with circular cross section, whose tip angle is larger than that of the concave tapered surface, and which is in close opposition to a tip of the positioning member. With this preferable configuration, even when the concave tapered surface is deformed and the positioning member attempts to enter the concave tapered surface beyond a certain position, the tip of the positioning member abuts the tapered surface, which has a large tip angle. Consequently, it can be prevented that the positioning member enters much beyond a certain position into the tapered portion. Therefore, it is possible to set a small moving stroke in the axial direction for the positioning member. As a result, even when the moving stroke for the positioning member in the axial direction is small, the rotator is pressed securely by the positioning member, and the rotator can be retained securely.
It is preferable that in the image forming apparatus according to the second configuration, the tip of the concave tapered surface at the coupling part contacting the positioning member during positioning and coupling is provided with a flat surface, which is in close opposition to a tip of the positioning member. With this configuration, even when the concave tapered surface is deformed and the positioning member attempts to enter the concave tapered surface beyond a certain position, the tip of the positioning member abuts the flat surface. Consequently, it can be prevented that the positioning member enters much beyond a certain position into the tapered portion. Therefore, it is possible to set an even smaller moving stroke in the axial direction for the positioning member. As a result, the moving stroke for the positioning member in the axial direction can be set to be short while retaining the rotator securely, so that the apparatus main body can be made smaller.
It is preferable that in the image forming apparatus according to the second configuration, the positioning member is made of a conductive material and is electrically grounded; the flange coupling with the positioning member is made of an insulating material; a center of a coupling part of the flange is provided with a through hole connecting an inner portion of the rotator with an outer portion thereof; and an electrode member is provided inside the through hole, which is retained while being biased in the direction of the positioning member, and which establishes conduction between the rotator and the positioning member by contacting the positioning member. With this preferable configuration, the electrode member contacts the positioning member at the rotation center of the coupling portion where the relative displacement amount is the smallest, so that a secure electrical conduction can be established also during rotation. In addition, the flange and the positioning member rotate together, and there is no relative movement in the rotation direction between the two, so that an even more secure electrical conduction can be established.
It is preferable that in the image forming apparatus according to the second configuration, the convex spherical tip of the positioning member is provided with a flat portion that is perpendicular to the rotation axis. With this preferable configuration, the contact between the electrode member and the positioning member, which contact each other elastically, can be made more reliable, so that electrical conduction can be established more securely. Furthermore, even when the stroke in the axial direction of the positioning member is short, it is possible to pull out the positioning member from the concave tapered surface of the flange. Moreover, since the concave tapered surface of the flange contacts the spherical surface of the positioning member over the entire perimeter of a circle, it is possible to retain the photosensitive member securely, even when the spherical surface of the positioning member is short. As a result, the apparatus main body can be made smaller, since the moving stroke of the positioning member can be made short.
It is preferable that the image forming apparatus according to the second configuration further comprises a driving motor for generating a rotation force for the rotator; and a rotation transmission member provided in one piece with one positioning member, wherein transmission and disconnection of the rotation force is performed by substantially coaxial rotation with that rotator that is positioned in the image forming position, and advancing and receding in the axial direction of the rotator; wherein the flange opposing the rotation transmission member has, on an end surface, a rotation follower portion to which a rotation force is transmitted when it contacts the rotation transmission member. With this preferable embodiment, the coupling portion on the driving side for transmitting the angular speed does not vary, and the rotation center of the rotator can be defined reliably. As a result, variations of the rotation speed of the rotator can be suppressed, and it is possible to obtain a good image without color misalignments. Moreover, in this case, it is preferable that a contact portion for contact between the rotation transmission member and the rotation follower portion extends through a center of the convex spherical surface of the tip of the positioning member, and is at a position perpendicular to a rotation center axis of the rotation transmission member. With this preferable embodiment, positional misalignments due to speed variations are suppressed, and a high-quality image can be obtained. Moreover, in this case, it is preferable that at least one of the contact faces where the rotation transmission member contacts the rotation follower portions is provided with a protrusion. With this configuration, the contact point is usually the tip of the protrusion and does not change, so that rotation speed variations of the rotator, which are caused by the contact portion where the rotation transmission member contacts the rotation follower portion, can be suppressed. As a result, positional misalignments for each color due to speed variations can be suppressed, and it is possible to obtain a high-quality image.
A third configuration of an image forming apparatus in accordance with the present invention comprises a plurality of image forming units having a rotator with flanges on both ends; a unit retaining member, which retains the plurality of image forming units, and switches the plurality of image forming units by moving them successively between an image forming position and a waiting position; an intermediate transfer member, which contacts the image forming unit positioned in the image forming position and successively accepts toner images of various colors from the image forming units, so as to form a colored toner image on its surface; a positioning member for coupling at a coupling part at a center of an end surface of at least one of the flanges of the rotator by advancing and receding in the axial direction when being substantially coaxial with the rotator of the image forming unit that is positioned in the image forming position; a driving motor for generating a rotation force for the rotator; and a rotation transmission member provided in one piece with one positioning member, for which transmission and disconnection of the rotation force is performed by substantially coaxial rotation with the rotator that is positioned in the image forming position, and advancing and receding in the axial direction of the rotator; wherein an end surface of the flange opposing the rotation transmission member is provided with rotation follower portions made of a plurality of concave and convex portions; and wherein the rotation transmission member is provided with one transmission tongue for transmitting a rotation force by meshing with the rotation follower portions. With this third configuration of an image forming apparatus, the angular speed is always transmitted by the same tongue, so that there are no variations in the angular speed transmitted to the photosensitive member.
It is preferable that in the image forming apparatus according to the third configuration, the rotation transmission member is provided with at least one protrusion portion of the same height as the transmission tongue; and during rotation, the at least one protrusion portion enters a concave portion of the rotation follower portions, but does not contact the rotation follower portions. With this preferable configuration, there is no resulting counter-force on the rotation transmission member when the transmission tongue hits the tips of the tongues on the flange. Thus, it is possible to move the rotation transmission member smoothly in the axial direction. As a result, the transmission tongue can be meshed securely with the rotation follower portions when the rotation starts.
A fourth configuration of an image forming apparatus in accordance with the present invention comprises a plurality of image forming units having a rotator with flanges on both ends; a unit retaining member, which retains the plurality of image forming units, and switches the plurality of image forming units by moving them successively between an image forming position and a waiting position; an intermediate transfer member, which contacts the image forming unit positioned in the image forming position and successively accepts toner images of various colors from the image forming units, so as to form a colored toner image on its surface; a positioning member for coupling at a coupling part at a center of an end surface of at least one of the flanges of the rotator by advancing and receding in the axial direction when being substantially coaxial with the rotator of the image forming unit that is positioned in the image forming position; a driving motor for generating a rotation force for the rotator; and a rotation transmission member provided in one piece with one positioning member, for which transmission and disconnection of the rotation force is performed by substantially coaxial rotation with the rotator that is positioned in the image forming position, and advancing and receding in the axial direction of the rotator; wherein an end surface of the flange opposing the rotation transmission member is provided with rotation follower portions made of a plurality of concave and convex portions; wherein the rotation transmission member is provided with a transmission tongue for transmitting a rotation force by meshing with the rotation follower portions; and wherein, when a tip of the transmission tongue reaches a tip position of the rotation follower portions during the transition from a disconnected state to a connected state for the rotation force, the positioning member has advanced inside beyond an edge portion of the coupling part. With this fourth configuration of an image forming apparatus, when the transmission tongue reaches the tip position of the rotation follower portions, the tip of the positioning member enters beyond an edge portion of the coupling part of the flange, so that at the portion where the tongue abuts, the rotator can be moved in a radial direction, and the positioning member can be coupled securely with a coupling part of the flange.
It is preferable that in the image forming apparatus according to the fourth configuration, the coupling part comprises a concave tapered surface with circular cross section, which contacts the positioning member during positioning and coupling; and a tapered surface with circular cross section, which is provided at a tip of the concave tapered surface, and whose tip angle is greater than that of the concave tapered surface.
It is preferable that in the image forming apparatus according to the fourth configuration, at least a tip of the transmission tongue of the rotation transmission member is movable in a rotation direction with respect to the positioning member and biased toward the rotator. With this preferable configuration, the radial movement of the rotator is not hindered when the positioning member abuts the coupling part. Consequently, the rotator can be positioned even more securely in the image forming position, and the rotation speed can be transmitted precisely. Moreover, in this case, it is preferable that the transmission tongue of the rotation transmission member is formed only in a portion in a rotation circumferential direction, and the rotation transmission member is retained rotatably with respect to the positioning member around a rotation shaft that is provided perpendicularly to the rotation center axis at a peripheral portion where the transmission tongue is not formed. With this preferable configuration, it does not become long in the rotation axial direction, even when the coupling and sliding portion between the rotation center and the rotation transmission member is set to be long. As a result, the length from the bearing of the positioning member to its tip can be set short and without clearance, so that the apparatus main body can be made smaller. In this case, it is furthermore preferable that the rotation transmission member is provided with a posture defining means for defining a posture of the rotation orientation of the rotation transmission member. With this preferable configuration, the tip of the transmission tongue does not hit the bottom of the rotation follower portions of the flange, and the transmission tongue and the rotation follower portions of the flange usually mesh at the proper position. Moreover, in this case, it is furthermore preferable that the rotation shaft is provided at a position directly near an end surface of the flange that opposes the rotation transmission member during positioning and coupling. With this configuration, even when there is an intersection angle xcex8 between the center axis of the driving shaft and the center axis of the rotator, the distance between the contact point where the transmission tongue contacts the rotation follower portions and the center axis of the driving shaft can be maintained substantially constant.
It is preferable that in the image forming apparatus according to the fourth configuration, a surface that opposes in the circumferential direction a surface where the transmission tongue and at least one of the rotation follower portions contact during rotation and driving is oblique in the circumferential direction. With this preferable configuration, the impact at the time of coupling during the moving in the axial direction can be reduced, and as a result, collision noise can be avoided.
It is preferable that in the image forming apparatus according to the fourth configuration, when a tip of the rotation transmission member reaches a tip position of the rotation follower portions while being moved toward the rotator, coupling between the positioning member and the coupling part is incomplete; and that at least one portion of the transmission tongue of the rotation transmission member is normally positioned between an outermost peripheral portion and an innermost peripheral portion of the rotation follower portions. With this preferable configuration, when the positioning member is moved toward the rotator and the rotator is being positioned, the inner peripheral surface of the tongues on the side of the positioning member cannot abut the outer peripheral surfaces of the tongues on the side of the rotator. Furthermore, the inner peripheral surface of the tongues on the side of the rotator cannot abut the outer peripheral surfaces of the tongues on the side of the positioning member. As a result, the rotator is moved securely in a radial direction, and the rotator can be positioned at its correct position.
A fifth configuration of an image forming apparatus in accordance with the present invention comprises a plurality of image forming units having a rotator with flanges on both ends; a unit retaining member, which retains the plurality of image forming units, and switches the plurality of image forming units by moving them successively between an image forming position and a waiting position; an intermediate transfer member, which contacts the image forming unit positioned in the image forming position and successively accepts toner images of various colors from the image forming units, so as to form a colored toner image on its surface; a driving motor for generating a rotation force for the rotator and the intermediate transfer member, which stops when the unit retaining member is being moved; a detection means for detecting a reference position of the intermediate transfer member after the driving motor has started; an exposure means for forming a latent image on the rotator, based on a detection signal from the detection means; a rotation transmission member for which transmission and disconnection of the rotation force is performed by substantially coaxial rotation with the rotator that is positioned in the image forming position, and advancing and receding in the axial direction of the photosensitive member; wherein an end surface of one of the flanges is provided in the circumferential direction with rotation follower portions made of a plurality of concave and convex portions, which transmit a rotation force by meshing with the rotation transmission member; wherein a pitch between neighboring concave and concave portions of the rotation follower portions is smaller than a rotation angle of the driving transmission member from the start of the driving motor until the generation of the detection signal. With this fifth configuration of an image forming apparatus, the reference position of the intermediate transfer member is detected after the driving tongue has meshed with the rotation follower portions, and after the speed of the intermediate transfer member has stabilized. As a result, the position of the image can be aligned precisely on the intermediate transfer member, because anomalous speed variations do not occur after the reference position has been detected.
It is preferable that in the image forming apparatus according to the fifth configuration, the pitch between neighboring concave and concave portions of the rotation follower portions is smaller than a rotation angle of the driving transmission member from the start of the driving motor until the acceleration of the driving motor to a predetermined speed. With this preferable configuration, the driving tongue and the rotation follower portions mesh while the driving motor is being accelerated. Therefore, the time from the meshing of the driving tongue and the rotation follower portions until the speed variations due to load variations have subsided becomes short. As a result, after the meshing of the driving tongue and the rotation follower portions, the speed of the intermediate transfer member stabilizes in a short time. As a result, if the reference position of the intermediate transfer member is detected after the driving motor is started, anomalous speed variations do not occur after the position has been detected, so that the positions of the images on the intermediate transfer member can be aligned precisely.
A second configuration of an image forming unit in accordance with the present invention comprises a rotator with flanges on both ends, and can be installed in and removed from an image forming apparatus comprising a unit retaining member, which retains a plurality of image forming units, and switches the plurality of image forming units by moving them successively between an image forming position and a waiting position; an intermediate transfer member, which contacts the image forming unit positioned in the image forming position and successively accepts toner images of various colors from the image forming units, so as to form a colored toner image on its surface; and a positioning member for coupling with at least one of the flanges of the rotator by advancing and receding in the axial direction when being substantially coaxial with the rotator of the image forming unit that is positioned in the image forming position, the tip of the positioning member being a convex spherical surface whose rotation center is the center axis; wherein a coupling part for coupling with the positioning member of the image forming apparatus is provided at the center of an end surface of the flanges; and wherein the coupling part is a concave tapered surface with a circular cross section having the axis of the rotator as a center axis.
It is preferable that in the image forming unit according to the second configuration, the tip of the concave tapered surface at the coupling part contacting the positioning member of the image forming apparatus during positioning and coupling is provided with a tapered surface with circular cross section, whose tip angle is larger than that of the concave tapered surface, and which is in close opposition to a tip of the positioning member.
It is preferable that in the image forming unit according to the second configuration, the tip of the concave tapered surface at the coupling part contacting the positioning member of the image forming apparatus during positioning and coupling is provided with a flat surface, which is in close opposition to a tip of the positioning member.
It is preferable that in the image forming unit according to the second configuration, the flange is made of an insulating material; a center of a coupling part of the flange is provided with a through hole connecting an inner portion of the rotator with an outer portion thereof; and an electrode member is provided inside the through hole, which is retained while being biased in the direction of the positioning member of the image forming apparatus, and which establishes conduction between the rotator and the positioning member by contacting the positioning member.
It is preferable that the image forming unit according to the second configuration further comprises a driving motor for generating a rotation force for the rotator; and a rotation transmission member provided in one piece with one positioning member, wherein transmission and disconnection of the rotation force is performed by substantially coaxial rotation with the rotator that is positioned in the image forming position, and advancing and receding in the axial direction of the rotator; and that the flange opposing the rotation transmission member has, on an end surface, a rotation follower portion to which a rotation force is transmitted when it contacts the rotation transmission member. Moreover, in this case, it is preferable that the contact portion between the rotation transmission member and the rotation follower portion goes through a center of the convex spherical portion of the tip of the positioning member at a coupling position, and is at a position perpendicular to a rotation center axis of the rotation transmission member. In this case, it is even more preferable that at least one of the contact faces where the rotation transmission member contacts the rotation follower portions is provided with a protrusion.
A third configuration of an image forming unit in accordance with the present invention comprises a rotator with flanges on both ends, and the image forming unit can be installed in and removed from an image forming apparatus comprising a unit retaining member, which retains a plurality of image forming units and switches the plurality of image forming units by moving them successively between an image forming position and a waiting position; an intermediate transfer member, which contacts the image forming unit positioned in the image forming position and successively accepts toner images of various colors from the image forming units, so as to form a colored toner image on its surface; a positioning member for coupling with at least one of the flanges of the rotator by advancing and receding in the axial direction when being substantially coaxial with the rotator of the image forming unit that is positioned in the image forming position; a driving motor for generating a rotation force for the rotator; and a rotation transmission member provided in one piece with one positioning member, and which has a transmission tongue for performing transmission and disconnection of the rotation force by substantially coaxial rotation with the rotator that is positioned in the image forming position, and advancing and receding in the axial direction of the rotator; wherein a coupling part for coupling with the positioning member of the image forming apparatus is provided at the center of an end surface of the flanges; wherein an end surface of the flange that opposes the rotation transmission member is provided with rotation follower portions made of a plurality of concave and convex portions; and wherein, when a tip of the transmission tongue reaches a tip position of the rotation follower portions during the transition from a disconnected state to a transmission state of the rotation force, the positioning member has advanced inside beyond an edge portion of the coupling part.
It is preferable that in the image forming unit according to the third configuration, the coupling part comprises a concave tapered surface with circular cross section, which contacts the positioning member during positioning and coupling; and a tapered surface with circular cross section, which is provided at the tip of the concave tapered surface, and whose tip angle is greater than that of the concave tapered surface.
It is preferable that in the image forming unit according to the third configuration, a surface that opposes in a circumferential direction a surface of the rotation follower portion that contacts the transmission tongue during rotation and driving is oblique in a circumferential direction.
It is preferable that in the image forming unit according to the third configuration, when a tip of the transmission tongue reaches a tip position of the rotation follower portions while being moved toward the rotator, coupling between the positioning member and the coupling part is incomplete; and that at least one portion of the transmission tongue of the rotation transmission member is normally positioned between an outermost peripheral portion and an innermost peripheral portion of the rotation follower portions.
A fourth configuration of an image forming unit in accordance with the present invention comprises a rotator with flanges on both ends, and the image forming unit can be installed in and removed from an image forming apparatus comprising a unit retaining member, which retains the plurality of image forming units and switches the plurality of image forming units by moving them successively between an image forming position and a waiting position; an intermediate transfer member, which contacts the image forming unit positioned in the image forming position and successively accepts toner images of various colors from the image forming units, so as to form a colored toner image on its surface; a driving motor for generating a rotation force for the rotator and the intermediate transfer member, which stops when the unit retaining member is being moved; a detection means for detecting a reference position of the intermediate transfer member after the driving motor has started; an exposure means for forming a latent image on the image forming unit, based on a detection signal from the detection means; a rotation transmission member for which transmission and disconnection of the rotation force is performed by substantially coaxial rotation with the rotator that is positioned in the image forming position, and advancing and receding in the axial direction of the photosensitive member; wherein an end surface of one of the flanges is provided in circumferential direction with rotation follower portions made of a plurality of concave and convex portions, which transmit a rotation force by meshing with the rotation transmission member; wherein a pitch between neighboring concave and concave portions of the rotation follower portions is smaller than a rotation angle of the driving transmission member from the start of the driving motor until the generation of the detection signal.
It is preferable that in the image forming unit according to the fourth configuration, a pitch between neighboring concave and concave portions of the rotation follower portions is smaller than a rotation angle of the driving transmission member from the start of the driving motor until the acceleration of the driving motor to a predetermined speed.